In a multitude of commercial applications, it is common to employ a heavy duty conveyor belt for the purpose of transporting product and material. The belts so employed may be relatively long, on the order of miles, and represent a high cost component of an industrial material handling operation. In many applications, the belts are susceptible to damage from the material transported thereby and a rip (slit, cut or tear) may develop within the belt. A torn or ripped belt can be repaired once detected. The cost of repairing a heavy duty conveyor belt and the cost of cleaning up material spilled from the damaged belt can be substantial. If, however, such a rip or tear commences and the belt is not immediately stopped, the rip can propagate for a substantial distance along the belt. It is, therefore, desirable to detect and locate a rip in the belt as quickly as possible after it commences and to immediately terminate belt operation, whereby minimizing the extent of the damage to the belt.
It is well known to employ sensors within conveyor belts as part of a rip detection system. In a typical system, sensors in the form of loops of conductive wire are affixed or embedded in the belt and provide a rip detection utility as part of an overall rip detection system. Rip detection is achieved through the inferential detection of an “open circuit” condition in one or more of the sensor loops in the belt. Typically an electrical energy source external to the belt is inductively or capacitively coupled to a sensor loop in the belt. A break in the conductive wire loop of the sensor may be detected by a remote transmitter/receiver (exciter/detector). Disposition of a plurality of such sensors at intervals along the conveyor may be effected with each sensor passing within read range of one or more exciter/detectors at various locations. A rip or tear will encounter and damage a proximal sensor loop and the existence of the tear will be detected when the proximal sensor loop damage is detected as an open circuit by the reader at its next pass. In this manner, the existence of a tear will be promptly detected and repaired and damage to the belt therefrom minimized.
U.S. Pat. No. 3,742,477 (Enabnit; 1973) discloses a “figure eight” sensor loop useful within belt sensor system. U.S. Pat. No. 4,854,446 (Strader; 1989) teaches a “figure eight” sensor loops disposed at intervals along a conveyor belt. U.S. Pat. No. 6,352,149 (Gartland, 2002) provides a system in which antennae are embedded in a conveyor belt to couple with an electromagnetic circuit consisting of two detector heads and an electronic package. Coupling occurs only when an antenna passes across the detector heads and can only occur when the loop integrity has not been compromised.
U.S. Pat. No. 6,715,602 discloses a sensor system in which sensors are embedded at predetermined intervals along a conveyor belt. A detector detects the presence or the absence of a sensor and that information is used to evaluate the condition of the belt at the sensor location. While the system works well, certain data interpretation problems exist. The RFID tags used in the belt and the information they provide are not reliable for use in drawing critical conclusions. If the tags are not read, the system is configured to shut the belt down. Such a disruption may or may not be necessary given the location of the tag in the belt and whether the failure to detect the tag should be interpreted as a belt failure.
It is, therefore, important that the system not shutdown automatically if the tag(s) are not detected. In addition, it is desired that the reading of sensors along the belt be synchronized in a reliable manner that minimizes the possibility of faulty identification of sensor location or faulty detection of sensor malfunction. This is important as the conveyor system ages and sensor operation becomes intermittent. Intermittent sensors can result in a contradiction between the memory map in the system and the actual position of a detected sensor in the belt. The system may find itself looking for a different embedded sensor in its memory than the actual sensor that is passing by the detector head(s). As a result, the detection system and memory map may become contradictory and unreliable.
It is, accordingly, a remaining need in the industry for a conveyor belt sensor system and method that can correlate exact belt position to the stored data within the sensor system (memory map). Such a system and method should be compatible for use in a wide range of available sensor systems for conveyor belts. The method and system, moreover, should be dependable and facilitate a reliable location of intermittent or non-functioning sensors in a belt. Moreover, a suitable method and system will dependably synchronize location of the belt with a memory map so as to minimize the possibility of erroneous sensor location identification.